1. Field of the Invention
The present invention relates generally to furnaces. More specifically, the present invention relates to a continuous process furnace having a plurality of heating zones for heat treating a substrate.
2. Description of Related Art
Today, many products are subjected to heat treating operations during production. The product undergoes heat treatment for many reasons, including thermal curing during semiconductor wafer fabrication, annealing operations to harden a material of the product, such as steel, or the like. Often times, the heat treatment process is carried out at very high temperatures. In order to carry out a heat treatment operation at these elevated temperatures, ovens are constructed capable of high operating temperatures.
In some cases, ovens used for heat treating were constructed of brick having a great amount of thermal inertia. These brick ovens typically had a rectangular configuration as shown with reference to FIG. 1 which illustrates a cross-sectional view of a brick oven 10 in accordance with the prior art. The brick oven 10 includes a rectangular cross-section through which products pass during heat treating. During a heat treatment operation, a uniform heating environment is preferred in order to ensure proper heat treating. Nonetheless, due to the rectangular cross section of prior art brick ovens, a uniform heating environment was difficult to achieve. Instead, pockets A1 through A4 and B typically formed within the cross section of the brick oven 10. The pockets A1 through A4 and B were of a different temperature than the rest of the cross section of the brick oven 10. Since the pockets A1 through A4 and B were at a different temperature, independent adjustments were required to maintain the pockets A1 through A4 and B at a uniform temperature with the brick oven 10. Additional zones were also required to maintain the pockets A1 through A4 and B at a uniform temperature. Therefore, additional components required for the individual adjustments along with the additional zones increased operating costs for brick ovens. Likewise, the increased amount of components decreased reliability since the increased amount of components increased the likelihood of failure. Moreover, due to the high amount of thermal inertia of the bricks used in the brick oven, the brick ovens required a great amount of time to come up to operating temperatures. As such, manufacturing costs associated with products using these ovens were increased due to the increased time and energy requirements of the ovens.
In order to address the issues associated with brick ovens, manufacturers started implemented ovens having lighter insulation and lower mass. The ovens using lighter insulation and lower mass included light gauge ovens having the rectangular configuration. Nonetheless, these light gauge ovens suffered the problems associated with brick ovens having a rectangular configuration.
These ovens included cylindrical heating elements having wires disposed therein which provided heat for the heating elements, as described in U.S. Pat. No. 4,596,922, the disclosure of which is herein incorporated by reference in its entirety, the prior art heating element included a cylindrical tube formed of a ceramic insulating material along with a wire disposed within the ceramic insulating material. The lightweight ceramic insulating material included good thermal characteristics while at the same time being deformable such that the wire expanded and contracted during operation without damaging either the wire or the ceramic insulating material.
During operation of the prior art heating element, the wire provided a source of heat for the heating element. As such, products passing through the heating element were subjected to a heat treatment operation, whereby the wire exposed the products to heat. Nonetheless, the configuration of the wire within the heating element minimized the thermal efficiency of the heating element. To further illustrate, prior art wires used in the heating elements had a small diameter, as such, the exposed surface area for heating a product was small. The small surface area of the wire required a high temperature of the wire in order to effectively heat products passing through the heating wires. As such, the higher temperatures necessitated increased amounts of energy supplied to the furnace, thereby increasing the overall costs associated with operating ovens using the prior art heating elements. In addition, the high temperatures required by prior art ovens decreased the reliability and efficiency of both the heating element and the furnace using the heating element. Likewise, reliability of these wires were further reduced since the temperature of the heating wire fluctuated during operation of the oven.
Therefore a need exists for a device which minimizes thermal fluctuations of a furnace during operation of the furnace. Moreover, this device should have increased reliability and minimal operating costs.
The present invention fills the aforementioned needs by providing a furnace with a heating section having a high mass. The mass of the heating section of the furnace is larger than a mass of the working components of the furnace.
In one embodiment of the present invention, a furnace for heat treating a substrate is disclosed. The furnace includes a heating section, a transport mechanism, an entrance assembly and an exit assembly. The heating section heat treats the substrate as the substrate passes through the furnace. The heating section includes heating coils which provide heat to the heating section. The transport mechanism, which is partially disposed within the heating section, transports the substrate through the heating section. The transport mechanism enters the heating section via the entrance assembly and exits the heating section via the exit assembly. The furnace also includes a processing chamber disposed within the heating section. A mass of the heating section exceeds a combined mass of a mass of the processing chamber disposed within the heating section, the transport mechanism and the substrate within the heating section.
In another embodiment of the present invention, a furnace for heat treating a substrate having a mass is disclosed. The furnace includes a heating section and working components. The heating section includes a plurality of heating coils and spacers disposed within the heating coils which heat treats the substrate. A mass of the plurality of coils and a mass of the spacers contributes to a heating section mass. The working components, which has a working component mass, includes a transport mechanism, an entrance assembly and an exit assembly. The transport mechanism, which is disposed within the heating section, transports the substrate through the heating section. A mass of the transport mechanism contributes to the working component mass. The entrance assembly, which is disposed adjacent the heating section, admits the substrate into the heating section via the transport mechanism. The entrance assembly includes a processing chamber which extends through the heating section. A portion of the processing chamber which extends through the heating section has a mass which contributes to the working component mass. The exit assembly, which allows exit of the substrate from the heating section, is disposed adjacent the heating section opposite the entry assembly. The heating section mass exceeds a combined mass of the substrate disposed within the heating section and the working component mass.
In yet another embodiment of the present invention, a furnace for heat treating a substrate is disclosed. The furnace includes an entry curtain section assembly for admitting the substrate into the furnace, an entrance assembly coupled with the entry curtain section assembly and a heating section coupled with the entrance assembly. The furnace also includes a transport mechanism disposed within the heating section, an exit assembly disposed adjacent the heating section opposite the entrance assembly, a cooling zone and an exit curtain section assembly coupled with the cooling zone. The heating section heat treats the substrate as the substrate passes through the furnace. The heating section, which has a mass, includes heating coils that provides heat to the heating section and spacers disposed within the heating coils. The transport mechanism transports the substrate through the heating section during heat treatment. The exit assembly facilitates exit of the substrate from the heating section and into the cooling zone, which is coupled with the exit assembly. The cooling zone includes a reverse flow heat exchanger which cools the substrate as the substrate passes through the cooling zone. The exit curtain section assembly facilitates exit of the substrate from the furnace upon cooling of the substrate. The heating section mass exceeds a combined mass of the transport mechanism, a processing chamber which extends through the heating section and the substrate within the heating section.
As may be appreciated, the present invention provides a furnace having a high mass heating section which exceeds a mass of the working components of the furnace. The high mass of the heating section relative to the working components minimizes thermal fluctuations of the furnace during heat treating operations and increases reliability of the furnace.